Plasma processing apparatuses are used to process substrates by techniques including etching, physical vapor deposition (PVD), chemical vapor deposition (CVD), ion implantation, and resist removal. One type of plasma processing apparatus used in plasma processing includes an inductively coupled plasma (ICP) chamber which has an RF antenna in the form of one or more RF coils to excite a process gas into the plasma state to process substrates in the chamber. Due to shrinking feature sizes and the implementation of new materials, improvement in plasma processing apparatuses to control the conditions of the plasma processing is required.
In ICP chambers, a ceramic window separates the chamber from the RF source, such as an RF antenna or RF coils. The brittle nature of the ceramic window material poses a limitation to the RF power used because as the RF power increases, heat flux into the ceramic window increases. The heat flux leads to temperature gradients, and thus internal stress in the ceramic window. Also, the distribution of heat flux can have a highly non-uniform distribution, which exacerbates the thermal stress problem.